Glossary

The One Number

The monthly figure Left Unspent is built around: what is safe to spend this month once everything already promised has been taken out. Income for a household, or revenue for a business, minus fixed bills, minus debt payments, minus the goals you're funding, equals the One Number. It is set once a month, and it is the only number you track.

Left unspent

What is left of the One Number right now. At the start of the month, left unspent equals the One Number, because nothing has been spent yet. As you spend on the card, the card balance comes off the One Number, and what remains is left unspent. It changes as often as you check it, it can never be more than the One Number, and it is the figure the app is named for.

Fixed costs

The costs already committed for the month before any discretionary spending: the bills that arrive whether or not you spend anything else. For a business, payroll is a fixed cost. They come out of income or revenue first, before the One Number is worked out.

Reserves

The umbrella term for everything set aside each month before the One Number is worked out: the goals you're funding, the bills that only come due once a year, and, for a business, the tax set-aside. In the app, a household's reserves appear as goals. Reserves come out before the One Number, so the money is already spoken for when the bill arrives.

The tax set-aside

A business reserve: a share of revenue put aside every month so the tax bill is already covered when it comes due. It is one of the reserves that come out before the One Number, so the number you spend against is already clear of what you owe.

The daily practice

Put discretionary spending on one dedicated card, and check that card's balance against the One Number as often as you like, to see what is left unspent this month. There is no logging and no categorizing. The One Number itself is set once a month. The practice is the glance at the balance.